1. Field of the Invention
The present invention relates to an image pickup apparatus and a lens apparatus capable of picking up still images.
2. Related Background Art
As a type of video camera intended to shoot moving pictures, there is proposed what is known as an interchangeable lens video camera (Japanese Patent Application Laid-Open No. H03-252638). Another related system can capture still images by using a mechanical shutter (Japanese Patent Application Laid-Open No. 2003-174584).
The functional configuration of this interchangeable lens video camera can be broadly divided into a camera body block and an interchangeable lens block. A camera microcomputer is built into the camera body block. On the other hand, the interchangeable lens block is equipped with a lens microcomputer. Between the camera microcomputer and the lens microcomputer, a format regarding communication is set in advance. Communication following this format takes place between the camera microcomputer and the lens microcomputer.
Where an image is shot with an interlace type CCD, the picked-up still images are field images.
Users of interchangeable lens video cameras, too, want to shoot not only fine moving images but also fine still images. This requirement has emerged in connection with the recent increases in the number of pixels used in CCDs and the capacity of memories, together with the advancement in image processing technology among other factors.
However, with a video camera having no mechanical shutter, the recently increased number of pixels has made it sometimes difficult to pick up still images. This is due to “differences in exposure time within a frame”.
This is particularly true of video cameras using interlace type CCDs. The following can be said of video cameras using interlace type CCDs where one image consists of one frame. In such a video camera, even-number charges and odd-number charges of scanning lines constituting each frame are alternately read out to form video signals for one image. Therefore, where a still image thereby formed has an information quantity of only one field (either even-number or odd-number charge information), it is impossible to obtain a still image of an adequate grade. If the still image generated had an information quantity of one frame, a fine still image could be obtained, but an interlaced field contains only half of the information quantity a full frame should have. For instance, where there is an information quantity of only one field, if there is a diagonal stripe on the object, the edge of that diagonal stripe will appear zigzag in the photographed image.